Magnetic material



June 22, 1948." A. L. w. WILLIAMS ETAL 2,443,756

I I MAGNETIC MATERIAL Filed Dec. 26, 1942 Hm Ha '3 Sheets-Sheet 2 lINVENTORS ALFRED L. W WILL/AMI ATTORNEY June 22, 1948 A; L. w. WILLIAMSET'AL 2,443,756

MAGNETKIC. MATERIAL Filed Dec. 26, 1942 Y s Sheets-Sheet s IiLl' IINVENTORS AL FRED AIM Mum/14s BY SEM/ JOJLPH BEGU/V ,4 ENE) PatentedJune 22, 1948 MAGNETIC MATERIAL Alfred 1;.-. w. Williams and Semi JosephBegun, Cleveland Heights, Ohio, assignors to The Brush DevelopmentCompany, Cleveland, Ohio, a corporation of Ohio A plication December 26,1942, Serial N0. 47 0,192

octane-;. (01. 274-4114) Our invention pertains to ail-improved magneticmaterial and the means and method for producing it. k

t is an object of ouri-nvention to providea magnetic material and themethod of making it wherein the material is endless andjointless.

It is another object of our-invention to provide an endless andjointlesspathofmagnetic material.

A further object of ourinvention isv toprovide an endless and jointlesspath comprised only of magnetic material.

Another object of our invention is to' provide an endless and jointlesspath oi-permanent magnetic material.

Further objects of ourinvention are: to provide the means and methodsfor producing improved magnetic materials.-

It is also an object of our invention to provide a magnetic path ofcontinuous solid magnetic material in which the crystallinemagneticmaterial is held together by intermolecular forces.

An object of our invention-is to provide a magnetic path composed ofsolidmagnetic material.

A "further object of our invention istoprovide a magnetic material whichcan be readily formed into difiicult shapes.

It has always been a problem toproduce agood magnetic tape. The chiefdifiicultyhas been-that good magnetic materials are hard and brittleandtherefore cannot be readily and cheaply worked into desired shapes, andsoft workable materials which can be readily worked-are usually not goodmagnetic materials; For exam-ple-ztungsten steel wire is a good magneticmaterial but it is so hard and tough that Carboloyrollersareused to workthe wire intoa flat tapes If softerrollers were used the wire wouldmake; grooves inthe rollers instead of the rollers fiattening the wireinto a tape. Obviously when special. rollers have to be used the processbecomes veryexpensive. Swedish magnetic tape hasbeen producedby rollinglarge sheets of the tungsten steel and then cutting from them narrowstrips .oftape. It is then necessary to polish-the cut edges to makethem smooth. This results in tape which, when obtainable, is veryexpensive.

Our invention makes possible the production of magnetic tapes. havingmagnetic qualities which are equal to or better than those of tun stensteel, and which can b'e'readily'w'orked, and which has the furtheradvantage that when an endless tape is desired no tapejoint nee'd. bepresent.

Other objects and-sinner"understanding of our invention may be had byreferring tovth'e following description and drawings in which:

Figure 1 illustrates an endless length of material having a joint.

Figure 2 shows an enlarged view of the joint portion of the'materialshown in Figure I after a-magnetic layer has been aifixed to thematerial.

Figure 3 shows another type of joint.

Figure 4 shows a disk.

Figure 5 shows an enlarged View of a, portion, of the disk of Figure 4'after a magnetic material has been afiixed.

Figure 6 illustrates a'thin endless band of magnetic material such asmay be obtained by stripping the base material from the composite tapeof Figure 1.

Figure 7 illustrates a method oi treating magnetic material byresistance heating.

Figure Sillustrates a method of treating a magnetic material byinduction heating.

Figure 9 illustrates a method of treatihg-amagnetic material byflame'heating.

Figure 10 shows a'process of heat treatingseve eral materials toestablish in them the best magnetic characteristics.

Figure 11 shows another process somewhat similar to the-processof Figure10.

Figure 12 shows another form oimagnetictape material.

Figures 13 and l show a. method of-iormihg an improved magnet, and

Fig. 15 shows a type of tape joint.

With reference to Figures 1 and 2, our-invention comprises providingaleng'th of non-magnetic material Iii;- s'uch' as copper or a copperal1oy.which has been formed into an endless-loop by joining the two freeendstogether'atf6, and depositing or otherwise aflixing to thenon-magnetic material a permanentlymagnetizable ferromagnetic materialll', such as cobalt or nickel, or a-cobalt nickel alloy, to establish acomposite magnetic recording medium. When the joint-l6 is properly madeand the magnetic material 11' is properly applied over the jointl-dtherewillbe no tape joint click caused by the joint lfiwhen a recordis reproduced from the composite magnetic recording medium. As shown inFigure 2 we prefer to use a diagonal butt joint as this pro: vides amaximum strength due to' a large area of contact between the two ends ofthe tape 15; and also reduces the physical displacement of the recordingand reproducing head pole pieces which lap joints often cause.

While we have shown an endless length of material in Figures 1 and 2 itis to be understood that our invention is not to be limited to endlessmaterials but may just as well be used with a length of material havingtwo free ends.

The magnetic layer depositing of the invention includes electroplating,vacuum sputtering, evaporation, chemical plating, or any other processwhich produces a continuous layer of permanently magnetizableferro-magnetic material, such as cobalt, nickel, ortheir alloys, andthereafter, if necessary, heat treating the deposited material toimprove its magnetic properties. Some materials which are deposited onthe base material need no heat treatment.

Figure 3 illustrates a butt joint it which is covered, by a magneticlayer on the order of several mils thick, and which has a connectingplate 22 for providing a more secure joint. The plate 22 is preferablyglued or otherwise affixed to each end of the base material l5 prior todepositing the magnetic layer IT. This arrangement is particularlyadaptable for use with magnetic recording and reproducing heads whichcontact only one side of the magnetic record track.

Our invention may also be utilized with disks is of material as is shownin Figures 4 and 5. The disk 18 is composed of non-magnetic materialsuch as paper, plastic, or metal, and the layer ll of magnetic materialis deposited on it in any of the aforesaid manners. One of the chiefreasons for plating a. non-magnetic disk with magnetic material insteadof using a disk of rolled magnetic material is to obtain a more uniformsignal response. The process of rolling a magnetic material results inimparting to the material a preferred magnetic direction. For thisreason a disk which has been rolled will not exhibit uniform magneticcharacteristics throughout a given path around its center. Our processof depositing the layer ll of magnetic material on a nonmagnetic diskresults in a composite magnetic disk which will exhibit uniform magneticcharacteristics throughout a given path around its center.

Figure 6 illustrates an endless and jointless magnetic tape consistingonly of magnetic material. It is formed by the plating process described in connection with Figure 2, and then re moving the basematerial. If the base material is inflammable, it may be burned ofi ifcare is taken to keep the temperature below the melting point of themagnetic material. In? the base-is wax it may be removed by heating orby dissolving it in a solvent. tricity such as paper is used as a basematerial upon which the magnetic material is to be deposited, it isnecessary to first coat one side of the paper with a conductor such asgraphite. The magnetic material will then be deposited on the graphitecoating. After a suitably thick coating has been obtained and the paperbase removed, most of the graphite can be wiped or scraped ofi of themagnetic material.

Figure 7 illustrates a method of heat treating the magnetic tape [9 ifit is made of an alloy whose magnetic properties are improved byheating. This heating method comprises rotating the tape over rollerswhich are connected to a source of current such as the transformer 20.The temperature to which the tape will be heated depends upon thecurrent passed through it, the resistance of the tape, and the rate ofrotation. By proper design these factors can 'be established to resultin the amount of heat in the tape which will,

If a non-conductor of elecupon cooling, give the tape its best magneticcharacteristics.

Another method of heating the tape is by induction as is shown in Figure8. The tape I9 is driven about rollers by the motor, and passes aninduction coil 2| which is connected to a source Of high frequencyalternating current. For best results the axis of the coil 2| should benormal to the plane of a broad face of the tape IS. A particularlyvaluable feature of induction heating is that for thick magneticmaterials the depth to which the tape is heated can be accuratelycontrolled. This advantage is most fully realized when a thick compositemagnetic recording medium is heat treated, and where the base materialcannot withstand the high temperature to which it is desired to heat thesurface of the magnetic material. For instance; the base material may beberyllium-containin copper in order to give the composite magneticrecording medium strength and resistance to fatigue, and the magneticmaterial maybe platinum-containing cobalt. This base material cannotwithstand temperatures much in excess of 800 degrees centigrade, whileit is necessary to heat this particular magnetic material to about 1100degrees centigrade in order to realize its maximum magneticcharacteristics. By using induction heating and controllin the depth ofpenetration of the heat it may be practical to use the combination of abase which cannot withstand high temperatures and a magnetic materialwhich must be heated to a high temperature. There is now available a newtype of steel which has a high melting point, and which has a mu between1.2 and 1.5. This steel also has relatively poor electricalconductivity, is machinable, and, has good fatigue resisting qualitieswhich makes it an ideal base material.

A third method of heating the tape is by an open flame such as is shownin Figure 9. In using this method, care must be exercised to assure aconstant heating of the tape or different portions might have differentmagnetic characteristics. By applying the heat at one of the rollers, itis possible to maintain the base material l5 at a lower temperature thanthe magnetic layer l1.

Figures 10 and 11 show two methods of continuously heat treatingcomposite magnetic recording mediums. In Figure 10, two layers ofpermanently magnetiz-able materials 25 and 26 are deposited on a basematerial 21 by electroplating or by chemical plating. It may benecessary, in order to deposit two or more layers of material, to runthe base material 21 through several successive plating processes, onefor each material deposited. The two layers 25, 26 may be formed ofcobalt and nickel, respectively, and the base material 21 may be copperor a copper alloy. Sputtering or evaporation could be used forsimultaneously depositing two or more different materials. After the twomaterials have been deposited the tape is run over two rollers 28, 29 towhich is connected a battery 30 or other current source suitable lfOIestablishing a high temperature in the tape between the rollers 28, 29.The temperature established must be sufficient to cause the two platedmaterials 25, 26, such as cobalt and nickel, to diffuse into each otherand form one or more alloy materials, such as a cobalt nickel alloy.After the plated materials have been fused into an alloy, the compositetape is quenched in the tank 3|. If the alloy is one which requiresfurther heat treating to establish its best magnetic qualities, weprovide a subsequent heat anew-e treatingistep which is percformed byresistance heatingv of. thetapebetween the. rollers .32, tit-by the.battery. 34.. Immediately after the. tape. is heated itisquenched inthe. tank 35. A coil 3% isplacedaround the tape at the. surface of thequenching fluidfor establishingin the successive portions ofrthe tape auniform magnetization at the :instanttlre portion is quenched.

In making flexible magnetic recording tracks, such as tapes, with a baseor core of substantially non-magnetic metal of high tensile strength, athin layer or the magnetic material of the requiredhigh coercive forceis deposited by plating on the core, and thereafter an additional thinlayer of magnetic material is deposited on the firstlayer, and so forth,until the desired overall thickness of the. magnetic layer is reached.

Theprocess of Figure 11 differs from the process of Figural!) in that itis designed to heat treat only the magnetic materials and not the basematerial. This .processmay. be used if it is not practical to use. .abase material which will withstand the. high temperatures. necessary tocause the layers 25, 26 to fuse or where the temperature necessary tocause fusion is high enough to cause some of the base material to enterinto the alloy and thereby spoil its magnetic characteristics. A knife31 is shown for separating the deposited layers and the base. It is tobe understood, however, that any of the aforementioned methods ofseparation can be used. After the alloy has been treated by the battery34 and quenched in a magnetic field established by the coil 36, the samebase 21, or a different base, can be joined to the magnetic alloy toestablish once again a composite magnetic tape.

Figure 12 illustrates a composite magnetic tape which is cformed of abase material 15 upon which two or more magnetic layers 38, 39 areformed. A tape of this kind is particularly adapted for push-pullmagnetic recording and reproducing such as is shown in the co-pendingBegun application Serial Number 596,481, filed May 29, 1945, or formulti-channel recording.

Figure 13 illustrates a plurality of thin magnetic strips formedaccording to any of the previously described methods, and positionedface-toface with respect to each other with each of the strips above thebottom strip slightly longer than the underneath one. Thus, when theplurality of strips are bent into a horseshoe, as is shown in Figure 14,the ends will be even and a laminated magnet will be formed in whichthere is a continuous magnetic path from one end to the other. This sameprocess can be used to form a magnet of practically any difficultconfiguration. It may also be used for making transformer cores. Eachlamination may be solid magnetic material, or may be magnetic materialconnected to a base material as has been described previously,

Figure 15 shows a type of joint in a magnetic material which producesmuch less tape joint discontinuity than existing tape joints. It isformed by butting two free ends of the tape together and connecting themtogether with the plate 22, without using any welding or solderingmaterial between the ends of the tape or between the tape and theconnecting plate. The only magnetic discontinuity in the signal will beoccasioned by the very small air gap 4| between the ends of the tape. Ifwelding or soldering had been used the magnetic discontinuity in thesignal would be much greater due to the heating of the ends of the tape.Even very carefully controlled heating using heat conductive material incontact with the tape to reduce-heattransmission back along the taperesults in a relatively long portion of the tape which has been heatedand cooled. This heating and cooling establishes amagnetic discontinuitywhich results in a click in a reproduced audible signal which isconsiderably greater than any click caused by a solderless butt-jointsuch as is shown in Figure 15. In accordance with the James-Millerapplication Serial No. 43?,350 issued on March--21, 1944, as Patent No.2,344,615,11he joint-can also be a diagonal butt or a lap joint.

The expression magnetic record transducing as used hereininthe-specification and claims is intended to mean either the operation ofmagnetically recording signals on --a magnetic recording medium, ortheoperationof reproducing magnetically recorded signals, or the operationof erasing magnetically recorded signals, orany combination of twoormore or these operations.

Although we'havedescribed-our invention with a certaindegreeofparticularity, it is to be understood that thepresentdisclosurehas been made only by wayof example and that numerous changes in thedetails of construction and the combination and arrangement of parts maybe resorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

We claim:

1. In a magnetic record transducing system for transducing signals on anelongated permanently magnetizable record track by magnetic fiux linkagebetween magnetic record transducing structure and successive elements ofa record member contacting the structure: a record member comprising anelongated flexible and thin core having a joint at which end portions ofthe core are secured together to form an endless core structure and apermanently magnetizable record-receiving coating adherently affixed tothe core and over the joint forming a continuous endless magnetic recordtrack extending smoothly and continuously thereover and free ofirregularities that vary the magnetic linkage with the transducerstructure along the region of the joint.

2. A magnetic transducing system as recited in claim 1 in which the coreis metallic.

3. A magnetic transducing system as recited in claim 2 in which therecord member is in the form of a fiat tape.

4. A magnetic transducing system as recited in claim 1 in which thecoating is a mixture of cobalt and nickel.

5. A magnetic transducing system as recited in claim 4 in which therecord member is in the form of a fiat tape.

6. A magnetic transducing system as recited in claim 1 in which the coreis metallic and the coating is a mixture of cobalt and nickel.

'7. A magnetic transducing system as recited in claim 6 in which therecord member is in the form of a fiat tape and the coating is anelectrolytically deposited mixture.

8. A magnetic transduoing system as recited in claim 1 in which therecord member is in the form of a flat tape.

9. A magnetic transducing system as defined by claim 1, in which thecore joint is provided with a smoothly continuous record track engagingsurface to which the record track is affixed.

ALFRED L. W. WILLIAMS. SEMI JOSEPH BEGUN.

(References on following page) REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS 5 Number Name Date 836,339 Pedersen Nov. 20, 1906880,484 Edison Feb. 25, 1908 934,601 Fuller Sept. 21, 1909 10 1,074,424Fessenden Sept. 30, 1913 1,173,951 Graef Feb. 29, 1916 1,285,996 HensleyNov. 26, 1918 1,425,184 Edison Aug. 8, 1922 1,488,186 Young Mar. 25,1924 15 1,653,467 ONeill Dec. 20, 1927 1,709,268 Hutchins Apr. 16, 19291,764,120 Robbins June 17, 1930 1,775,981 Warner Sept. 16, 19301,847,860 Best Mar. 1, 1932 an 2,002,151 Maurer May 21, 1935 2,039,372Wickmann May 5, 1936 2,059,783 Farnworth Nov. 3, 1936 2,074,281 SummerMar. 16, 1937 Number Number 8 Name Date Derby July 13, 1937 Loewe Apr.19, 1938 Ford July 4, 1939 Bitter July 4, 1939 Schaarwachter July 25,1939 Hopkins Feb. 27, 1940 Berry Apr. 23, 1940 Given Apr. 1, 1941 ChaseApr, 15; 1941 Whiley May 27, 1941 Gillett July 8, 1941 James et a1. Mar.21, 1944 FOREIGN PATENTS Country Date Great Britain June 20, 1930 GreatBritain Jan. 8, 1931 Great Britain Nov. 30, 1933 Great Britain Sept. 22,1936 Great Britain Oct. 28, 1937 Germany Sept. 7, 1933 Germany July 3,1937

